// The groups as the menu and the pages share them: the last group opened on this
// device (outside a group, the tools of the menu aim at it), and the views
// already read (the menu counts the documents of the current group).
import { api, ApiError } from './api';
import type { GroupView, Tool } from './group';

const KEY = 'ld:group';

/** The last group opened, read straight from storage (usable before any mount). */
export function lastGroup(): string | null {
  try {
    return localStorage.getItem(KEY);
  } catch {
    return null;
  }
}

/** Where a tool leads: its page in the group, or home when no group is known. */
export function toolHref(tool: Tool, group: string | null): string {
  return group ? `/g/${group}/${tool}` : '/';
}

class Groups {
  last = $state<string | null>(null);
  views = $state<Record<string, GroupView>>({});
  private asked = new Set<string>();
  private running = new Map<string, Promise<GroupView>>();

  init() {
    this.last = lastGroup();
  }

  /** Read a group (a read already under way is shared); one that opens becomes the last group. */
  load(slug: string): Promise<GroupView> {
    const running = this.running.get(slug);
    if (running) return running;
    this.asked.add(slug);
    const p: Promise<GroupView> = this.fetch(slug).finally(() => {
      if (this.running.get(slug) === p) this.running.delete(slug);
    });
    this.running.set(slug, p);
    return p;
  }

  private async fetch(slug: string): Promise<GroupView> {
    try {
      const v = await api.get<GroupView>(`/groups/${slug}`);
      this.views[slug] = v;
      if (v.group.open) this.remember(slug);
      else if (this.last === slug) this.forget();
      return v;
    } catch (e) {
      // A group that no longer shows or opens is no longer the last group; a network hiccup keeps it.
      if (this.last === slug && e instanceof ApiError && (e.code === 'not_found' || e.code === 'forbidden')) this.forget();
      throw e;
    }
  }

  /** Read a group once, for the menu; errors stay silent there. */
  ensure(slug: string) {
    if (this.views[slug] || this.asked.has(slug)) return;
    this.load(slug).catch(() => {});
  }

  remember(slug: string) {
    this.last = slug;
    try {
      localStorage.setItem(KEY, slug);
    } catch {
      /* no storage: the menu simply leads home */
    }
  }

  /** On sign-out, or when the last group no longer opens. */
  forget() {
    this.last = null;
    try {
      localStorage.removeItem(KEY);
    } catch {
      /* no storage */
    }
  }

  /** On sign-out: nothing read under the previous identity is kept. */
  reset() {
    this.forget();
    this.views = {};
    this.asked.clear();
    this.running.clear();
  }
}

export const groups = new Groups();